On Mon, 21 Sep 2026, Nicolas Frattaroli wrote:
> From: Derek Foreman <[email protected]>
>
> Add VTEM EMP generation to enable variable refresh rate signalling over
> HDMI.
>
> These infoframes are only generated if the sink supports VRR.
>
> Signed-off-by: Derek Foreman <[email protected]>
> Signed-off-by: Nicolas Frattaroli <[email protected]>
> ---
> drivers/gpu/drm/display/drm_hdmi_state_helper.c | 60
> +++++++++++++++++++++++++
> include/drm/drm_connector.h | 5 +++
> 2 files changed, 65 insertions(+)
>
> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> index d55548399687..33d0c9491643 100644
> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
> @@ -853,6 +853,56 @@ static int hdmi_generate_hdmi_vendor_infoframe(const
> struct drm_connector *conne
> return 0;
> }
>
> +static int hdmi_generate_emp_infoframe_vtem(const struct drm_connector
> *connector,
> + struct drm_connector_state
> *conn_state)
> +{
> + const struct drm_display_info *info = &connector->display_info;
> + const struct drm_crtc_state *crtc_state =
> + drm_atomic_get_crtc_state(conn_state->state, conn_state->crtc);
> + struct drm_connector_hdmi_infoframe *infoframe =
> + &conn_state->hdmi.infoframes.vtem;
> + struct hdmi_emp_infoframe_vtem *vtem =
> + &infoframe->data.vtem;
> + const struct drm_crtc_vrr_state *vrr = &crtc_state->vrr_state;
> + int vfront;
> +
> + infoframe->set = false;
> +
> + if (!connector->hdmi.funcs->vtem.write_infoframe)
> + return 0;
> +
> + if (!info->hdmi.vrr_capable)
> + return 0;
> +
> + hdmi_emp_infoframe_vtem_init(vtem);
> + if (!crtc_state->vrr_enabled || vrr->vic) {
> + vtem->base_refresh_rate = 0;
> + vtem->base_vfront = 0;
It shouldn't hurt to always populate base_refresh_rate and base_vfront,
might be cleaner to skip this check.
> + } else {
> + vtem->base_refresh_rate = drm_mode_vrefresh(&crtc_state->mode);
> + vfront = crtc_state->adjusted_mode.crtc_vsync_start -
> + crtc_state->adjusted_mode.crtc_vdisplay;
> + if (vfront > U8_MAX || vfront < 0)
> + return -EINVAL;
> +
> + vtem->base_vfront = vfront;
> + }
> + vtem->fva_factor_m1 = 0;
> + infoframe->set = true;
> +
> + if (!crtc_state->vrr_enabled) {
I don't think we should use the vrr_enabled CRTC property to determine
VRR_EN in the VTEM EMP. Transitioning the VRR mode sink-side typically causes
blanking, and it was discussed in patch [03/25] that drivers should be
free to handle vrr_enabled changes as a seamless switch since it only
concerns source-side VRR state (this is how the NVIDIA driver handles it).
Maybe it would make sense to extend the qms_enabled connector property
introduced in this patchset to an enum of {Off, Gaming, QMS}? This would allow
a standard path to control the VRR state on the sink, separately from
vrr_enabled.
> + vtem->m_const = false;
> + vtem->game_vrr_en = false;
> + return 0;
> + }
> +
> + vtem->game_vrr_en = true;
> +
> + vtem->m_const = !vrr->dynamic;
> +
> + return 0;
> +}
> +
> static int
> hdmi_generate_infoframes(const struct drm_connector *connector,
> struct drm_connector_state *conn_state)
> @@ -884,6 +934,10 @@ hdmi_generate_infoframes(const struct drm_connector
> *connector,
> if (ret)
> return ret;
>
> + ret = hdmi_generate_emp_infoframe_vtem(connector, conn_state);
> + if (ret)
> + return ret;
> +
> return 0;
> }
>
> @@ -1494,6 +1548,12 @@ int
> drm_atomic_helper_connector_hdmi_update_infoframes(struct drm_connector *con
> goto out;
> }
>
> + if (info->hdmi.vrr_capable)
> + ret = write_or_clear_infoframe(connector,
> + &funcs->vtem, "VTEM",
> + &old_conn_state->hdmi.infoframes.vtem,
> + &new_conn_state->hdmi.infoframes.vtem);
> +
> out:
> mutex_unlock(&connector->hdmi.infoframes.lock);
> return ret;
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index e561a444515f..6e431eb81705 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -1180,6 +1180,11 @@ struct drm_connector_hdmi_state {
> * matching our state.
> */
> struct drm_connector_hdmi_infoframe hdmi;
> +
> + /**
> + * @vtem: VTEM EMP infoframes structure matching our state.
> + */
> + struct drm_connector_hdmi_infoframe vtem;
> } infoframes;
>
> /**
>
> --
> 2.55.0
>
>
